Outboard engine system

ABSTRACT

In an outboard engine system, an inertia force a generated longitudinally by a piston  14  is countervailed by an inertia force b generated by a crankshaft  15 , and inertia forces c and d subsidiarily laterally generated vibrate a body of the outboard engine system laterally about a phantom center point C of vibration. At this time, an elastomeric member  74  resiliently supporting the system body on a hull has a rigidity in a tangent direction (in the direction of L 3 ) about the phantom center point C of vibration, which is set to be lower than a rigidity in a radial direction (in the direction of L 2 ) about the phantom center point C of vibration. Therefore, the lateral vibration is reduced effectively due to the lower rigidity of the elastomeric member  74 . Thrusts e and f generated by a propeller and acting in a longitudinal direction (in the direction of L 1 ) are transmitted to the hull through the elastomeric member  74 . However, the rigidity of the elastomeric member  74  in the longitudinal direction is set to be higher and hence, the thrusts e and f can be transmitted effectively to the hull.

FIELD OF THE INVENTION

The present invention relates to an outboard engine system including anengine having a crankshaft disposed vertically and a cylinder axisdisposed longitudinally.

BACKGROUND ART

In general, an outboard engine system includes a body frame on which anengine is mounted, and which is detachably mounted to a hull through amounting bracket. The engine is mounted vertically on the body framewith a crankshaft facing vertically and with a cylinder axis facinglongitudinally, so that the transmission of a power to a drive shaftdisposed vertically within the body frame can be conducted easily.

The vibration generated by the operation of the engine is transmittedfrom the body frame through the mounting bracket to the hull, but toreduce the vibration, the body frame is supported on the mountingbracket through an elastomeric member. A thrust generated by a propellerof the outboard engine system is transmitted from the body frame throughthe elastomeric member to the mounting bracket and further transmittedfrom the mounting frame to the hull. Therefore, it is required that theelastomeric member should meet conflicting demands that the thrustgenerated by the propeller is transmitted effectively from the bodyframe to the mounting bracket, while the transmission of the vibrationfrom the body frame to the mounting bracket is reduced effectively.

One of techniques for meeting the demands is to reduce the vibrationitself generated by the engine. For example, in a 2-cylinder and 4-cycleengine, it is common that two pistons are disposed at the same crankphase, and the ignition is conducted at equal intervals with ignitiontimings displaced by 360°. To reduce the primary vibration generated bythe engine, an outboard engine system has been proposed in JapanesePatent Application Laid-open No.63-192693, in which the rotational massof counterweights of the crankshaft relative to the reciprocation massof the piston is determined at 50%, and a balancer shaft reversed at thesame speed as the crankshaft has the remaining 50%.

Another technique for meeting the demands is to ensure that the rigidityof the elastomeric member supporting the body frame to the mountingbracket has an anisotropy. Thus, an outboard engine system has beenproposed in Japanese Patent Application Laid-open No.2-37096, whereinthe rigidity of an elastomeric member is set to be large in a directionto transmit a thrust generated by a propeller to a hull (i.e., in alongitudinal direction) and small in a direction perpendicular to suchdirection (i.e., in a lateral direction), thereby preventing thetransmission of the lateral vibration to the hull, while permitting thethrust to be transmitted effectively to the hull.

However, the outboard engine system described in Japanese PatentApplication Laid-open No.63-192693 suffers from not only a problem thatit is necessary to add a special balancer device and hence, the weightand the cost are increased, but also a problem that a power transmittingsystem such as a gear for driving a balancer shaft in operativeassociation with a crankshaft generates a noise.

The outboard engine system described in Japanese Patent ApplicationLaid-open No.2-37096 suffers from the following problem: The elastomericmembers are disposed at two points on opposite sides of a vertical axis(a torque rolling axis) extending through the center of gravity of theengine, so that a torque reaction generated in the crankshaft with theoperation of the engine can be supported. For this reason, the positionsof the elastomeric members are at a central portion of the outboardengine system and are liable to interfere with other equipments. This isinconvenient in respect of the layout.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished with the above circumstancesin view, and it is an object of the present invention to provide anoutboard engine system, wherein a thrust generated by a propeller can betransmitted effectively to a hull, while effectively reducing thetransmission of the vibration generated by an engine.

To achieve the above object, according to the present invention, thereis provided an outboard engine system comprising a system body, anengine mounted on the system body, a mounting means detachably mountedto a hull, and a mount device having a pair of left and rightelastomeric members for supporting the system body on the mountingmeans, characterized in that the engine is disposed, so that acrankshaft is disposed vertically, and a cylinder head disposed to facerearwards with a cylinder axis disposed in a longitudinal directionparallel to a propeller shaft, and so that a rate of balance between thereciprocal inertia mass of a piston and a rotational inertia mass of thecrankshaft is set at approximately 100%; the elastomeric members aredisposed on left and right opposite sides of the engine, and therigidity of the mount device is set so that the rigidity in a tangentdirection about a phantom center point of vibration in a high rotationalspeed range of the engine is lower than the rigidity in a radialdirection about the phantom center point of vibration.

With the above arrangement, a longitudinal inertia force generated bythe reciprocal inertia mass of the piston is converted into a lateralinertia force by the rotational inertia mass of the crankshaft. Thelateral inertia force vibrates the system body having the engine mountedthereon laterally about the phantom center point of vibration. At thistime, the rigidity of the mount device having the elastomeric membersdisposed on left and right opposite sides of the engine to resilientlysupport the system body on the mounting means mounted on the hull isset, so that the rigidity in the tangent direction about the phantomcenter point of vibration is set to be lower than the rigidity in theradial direction about the phantom center point of vibration and hence,the lateral vibration about the phantom center point of vibration can bereduced effectively due to the low rigidity of the mount device toimprove the riding comfort on the hull. A thrust acting in thelongitudinal direction parallel to the propeller shaft is transmitted tothe hull through the mount device, but the rigidity of the mount devicein the direction of the thrust is set at a high value and hence, thethrust can be transmitted effectively to the hull due to the highrigidity of the mount device.

In addition to the above arrangement, there is also provided an outboardengine system, wherein an angle formed by a straight line extendingforwards from the phantom center point of vibration with a straight lineextending from the phantom center point of vibration toward theelastomeric member is smaller than 45°.

With the above arrangement, the angle formed by the straight lineextending forwards from the phantom center point of vibration with thestraight line extending from the phantom center point of vibrationtoward the elastomeric member is smaller than 45°. Therefore, thedeviation between the direction of the thrust (the direction of thestraight line extending forwards from the phantom center point ofvibration) and the direction in which the rigidity of the mount deviceis highest (the direction of the straight line extending from thephantom center point of vibration toward the elastomeric member) can bedecreased, whereby the thrust can be transmitted further effectively tothe hull.

According to the present invention, there is provided an outboard enginesystem comprising a system body, an engine mounted on the system body, aswivel shaft for pivotally supporting the system body on a hull, a mountarm integral with the swivel shaft, a mount device having a pair of leftand right elastomeric members for supporting the system body on themount arm, and a steering handlebar connected to the mount arm to swingthe system body about the swivel shaft, characterized in that the engineis disposed, so that a crankshaft is disposed vertically, and a cylinderhead is disposed to face rearwards with a cylinder axis disposed in alongitudinal direction parallel to a propeller shaft, and so that a rateof balance between the reciprocal inertia mass of a piston and arotational inertia mass of the crankshaft is set at approximately 100%;the elastomeric members are disposed on left and right opposite sides ofthe engine; the rigidity of the mount device is set so that the rigidityin a tangent direction about a phantom center point of vibration in ahigh rotational speed range of the engine is lower than the rigidity ina radial direction about the phantom center point of vibration; and theswivel shaft is disposed on an arc of a circle extending through theelastomeric members about the phantom center point of vibration.

With the above arrangement, a longitudinal inertia force generated bythe reciprocal inertia mass of the piston is converted into a lateralinertia force by the rotational inertia mass of the crankshaft. Thelateral inertia force vibrates the system body having the engine mountedthereon laterally about the phantom center point of vibration. At thistime, the rigidity in the mount device having the elastomeric membersdisposed on the left and right opposite sides of the engine toresiliently support the system body on the hull is set, so that therigidity in the tangent direction about the phantom center point ofvibration is lower than the rigidity in the radial direction about thephantom center point of vibration and hence, the lateral vibration aboutthe phantom center point of vibration can be reduced effectively due tothe low rigidity of the mount device to improve the riding comfort onthe hull. A thrust acting in the longitudinal direction parallel to thepropeller shaft is transmitted to the hull through the mount device, butthe rigidity of the mount device in the direction of the thrust is setat a high value and hence, the thrust can be transmitted effectively tothe hull due to the high rigidity of the mount device. Moreover, theswivel shaft is disposed on the arc of the circle extending through theelastomeric members about the phantom center point of vibration andhence, the mount arm can be prevented from being swung about the swivelshaft by the vibration transmitted through the mount device to the mountarm, thereby suppressing the transmission of the vibration to thesteering handlebar connected to the mount arm to the minimum.

In addition to the above arrangement, there is provided an outboardengine system, further including a cover member fastened to a rearsurface of a lower end of an extension case connected to the system bodyto define a space with a horizontal section closed, and a mount blockwhich is mounted at a lower end of the swivel shaft and retained in thespace.

With the above arrangement, a box-shaped structure of a high rigiditywith the horizontal section closed is provided by fastening the covermember to the extension case and hence, the mount block can be firmedretained within the structure to effectively prevent the generation ofresonance.

Meanwhile, an engine-supporting block 41 in an embodiment corresponds tothe system body of the present invention; a mounting bracket 55 in theembodiment corresponds to the mounting means of the present invention;an upper mount 65 in the embodiment corresponds to the mount device ofthe present invention; an upper mount rubber member 74 in the embodimentcorresponds to the elastomeric member of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 14 show an embodiment of the present invention.

FIG. 1 is a side view of the entire arrangement of an outboard enginesystem;

FIG. 2 is an enlarged sectional view of an essential portion shown inFIG. 1;

FIG. 3 is a sectional view taken along a line 3—3 in FIG. 2;

FIG. 4 is an enlarged view of the essential portion shown in FIG. 1;

FIG. 5 is a sectional view taken along a line 5—5 in FIG. 4;

FIG. 6 is a sectional view taken along a line 6—6 in FIG. 2;

FIG. 7 is an enlarged sectional view of an essential portion shown inFIG. 6;

FIG. 8 is a sectional view taken along a line 8—8 in FIG. 7;

FIG. 9 is a sectional view taken along a line 9—9 in FIG. 7;

FIG. 10 is a perspective view of an upper mount rubber member;

FIG. 11 is an enlarged sectional view of the essential portion show inFIG. 1;

FIG. 12 is a view taken in the direction of an arrow 12 in FIG. 11;

FIG. 13 is a sectional view taken along a line 13—13 in FIG. 11; and

FIG. 14 is a diagram for explaining a vibration-reducing effect.

FIGS. 15 and 16 show a second embodiment of the present invention.

FIG. 15 is a similar to FIG. 12; and

FIG. 16 is a sectional view taken along a line 16—16 in FIG. 15.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described by way of embodiments withreference to the accompanying drawings.

As shown in FIGS. 1 to 3, a 2-cylinder and 4-cycle engine E mounted atan upper portion of an outboard engine system O includes a cylinderblock 11 integrally provided with a crankcase 11 ₁, a cylinder head 12coupled to the cylinder block 11, and a head cover 13 coupled to thecylinder head 12. Two pistons 14, 14 slidably received in two cylinderbores 11 ₂, 11 ₂ defined in the cylinder block 11 are connected throughconnecting rods 16, 16 to a crankshaft 15 supported in the cylinderblock 11.

A generator 17 and a recoil starter 18 are mounted coaxially on an endof the crankshaft 15 protruding upwards from the cylinder block 11. Acamshaft 20 is supported in a valve-operating chamber 19 defined betweenthe cylinder head 12 and the head cover 13, and a cam pulley 21 mountedat an upper end of the camshaft 20 and a crank pulley 22 mounted at anupper portion of the crankshaft 15 are connected to each other by atiming belt 23. An intake valve 26 and an exhaust valve 27 for openingand closing an intake port 24 and an exhaust port 25 defined in thecylinder head 12 respectively are connected to the camshaft 20 throughan intake rocker arm 28 and an exhaust rocker arm 29, respectively. Anair cleaner 30, a throttle valve 31 and a carburetor 32 disposed on aright side of the engine E are connected to the intake port 24.

An axis of the crankshaft 15 is disposed vertically, and axes of thecylinder bores 11 ₂, 11 ₂ are disposed longitudinally, so that a portionof each cylinder bore 11 ₂ on the side of the crankcase 11 ₁ facesforwards and a portion of each cylinder bore 11 ₂ on the side of thecylinder head 12 faces rearwards. The crank phases of the two pistons14, 14 are the same as each other, and the ignition timings provided bythe pistons 14, 14 are deviated from each other by 360°. Counterweights15 ₁ having a balance rate of 100% for opposing the reciprocal movementmass of the pistons 14, 14 are mounted on the crankshaft 15. Therefore,a longitudinal primary vibration generated with the reciprocal movementof the pistons 14, 14 is countervailed by the rotating movement of thecounterweights 15 ₁ of the crankshaft 15, and in place of it, a lateralprimary vibration is generated with the rotating movement of thecounterweights 15 ₁. The engine E is not provided with a balancer deviceother than the counterweights 15 ₁ of the crankshaft 15 and hence, thevibration generated by the engine E is small in the longitudinaldirection and large in the lateral direction.

An upper surface of an engine-supporting block 41 is coupled to a lowersurface of the engine E having the above-described structure. An uppersurface of an extension case 42 is coupled to a lower surface of theengine-supporting block 41, and an upper surface of a gear case 43 iscoupled to a lower surface of the extension case 42. An outer peripheryof the engine-supporting block 41 and an outer periphery of a lower halfof the engine E are covered with an undercover 44 coupled to an upperend of the extension case 42, and an upper half of the engine E iscovered with an engine cover 45 coupled to an upper end of theundercover 44.

The engine-supporting block 41 is integrally provided with an oil pan 41₁, and a suction pipe 47 provided with an oil strainer 46 isaccommodated in the oil pan 41 ₁. An exhaust passage-defining member 48is coupled to a rear surface of the engine-supporting block 41, and anexhaust gas expansion chamber 49 is defined in the extension case 42through a partition wall 42 ₁. An exhaust gas discharged from theexhaust port 25 is supplied through an exhaust passage 11 ₃ defined inthe cylinder block 11 into the exhaust passage-defining member 48 anddischarged therefrom into the outside water via the exhaust gasexpansion chamber 49 in the extension case 42 and a hollow in apropeller shaft 53 which will be described hereinafter.

A drive shaft 50 connected to a lower end of the crankshaft 15 is passedthrough the engine-supporting block 41, extends downwards within a driveshaft chamber 51 defined in the extension case 42, and is connectedthrough a forward/backward changeover mechanism 54 to a front end of thepropeller shaft 53 which is provided at its rear end with a propeller 52and supported longitudinally on the gear case 43.

As can be seen from FIGS. 4 and 5, a mounting bracket 55 for detachablymounting the outboard engine system O to a hull S includes an invertedJ-shaped mounting bracket body 56 and a set screw 57 threadedly engagedwith the mounting bracket body 56. A swinging arm 59 is pivotallysupported at its front end on the mounting bracket body 56 through apivot pin 58, and a pipe-shaped swivel case 60 is integrally coupled toa rear end of the swinging arm 59. A large number of pinholes 56 ₁ areprovided in the mounting bracket body 56, so that the tilting angle ofthe outboard engine system O about the pivot pin 58 can be regulated byinserting a pin 61 through a pinhole made in a locking plate 60 ₁ fixedto the swivel case 60 and any one of the pinholes 56 ₁ in the mountingbracket body 56.

A swivel shaft 62 relatively rotatably fitted in the swivel case 60includes a mount arm 63 and a mount block 64 at its upper and lowerends, respectively. The upper mount arm 63 is resiliently connected tothe engine-supporting block 41 through a pair of left and right uppermounts 65, 65, and the lower mount block 64 is resiliently connected tothe extension case 42 through a lower mount 66. A steering handlebar 67is fixed to a front end of the engine-supporting block 41, so that theengine-supporting block 41 can be swung laterally about the swivel shaft62 to steer the outboard engine system O by grasping the steeringhandlebar 67 to operate it laterally.

The structure of the upper mounts 65, 65 will be described below withreference to FIGS. 5 to 10 and 14.

The engine-supporting block 41 includes a pair of left and rightprotrusions 41 ₂, 41 ₂ overhanging forwards and upwards, and rubbermember-accommodating portions 71, 71 are formed on the protrusions 41 ₂,41 ₂, respectively. Each of the rubber member-accommodating portions 71,71 is a recess including an upper wall 71 ₁, a front wall 71 ₂, a rearwall 71 ₃, an outer wall 71 ₄ and an inner wall 71 ₅, and only a lowersurface thereof is opened. On the other hand, substantially rectangularparallelepiped upper mount rubber members 74, 74 are mounted to coverthe peripheries of metal cores 73, 73 fixed to left and right oppositeends of the mount arm 63 by bolts 72, 72. The upper mount rubber members74, 74 are fitted into the rubber member-accommodating portions 71, 71in the engine-supporting block 41 from below. Restraining lids 83, 83are fixed in the opened lower surfaces of the rubbermember-accommodating portions 71, 71 by bolts 84 to prevent the uppermount rubber members 74, 74 from being dropped from the rubbermember-accommodating portions 71, 71.

As can be seen from FIG. 14, a phantom center point C of a primaryvibration in a high rotational speed range (of 3,000 rpm or more) of theengine E lies at a rear portion of the outboard engine system O, and astraight line L₁ extending forwards from the phantom center point C ismatched with a cylinder axis. The outer walls 71 ₄, 71 ₄ and the innerwalls 71 ₅, 71 ₅ of the rubber member-accommodating portions 71, 71 areparallel to straight lines L₂, L₂ extending from the phantom centerpoint C of the primary vibration toward the centers of the upper mountrubber members 74, 74, respectively, and the front walls 71 ₂, 71 ₂ andthe rear walls 71 ₃, 71 ₃ of the rubber member-accommodating portions71, 71 are perpendicular to the straight lines L₂, L₂. Angles α, αformed by the straight line L₁ and the straight line L₂, L₂ are set atsmall values (smaller than 45°). Reference character L₃ indicates an arcof a circle extending through the centers of the upper mount rubbermembers 74, 74 about the phantom center point C, and the swivel shaft 62is located on the arc L₃.

As can be seen from FIG. 10, each of the upper mount rubber members 74includes upper and lower projections 75 and 76 located at front portionthereof and extending laterally, and upper and lower projections 77 and78 located at a rear portion thereof and extending laterally. Convexportions 75 ₁, 75 ₁ are further formed at opposite ends of theprojection 75 to protrude laterally; convex portions 76 ₁, 76 ₁ arefurther formed at opposite ends of the projection 76 to protrudelaterally; convex portions 77 ₁, 77 ₁ are further formed at oppositeends of the projection 77 to protrude laterally; and convex portions 78₁, 78 ₁ are further formed at opposite ends of the projection 78 toprotrude laterally.

The entire surfaces of the upper two projections 75 and 77 are in linecontact with the front wall 71 ₂ and the rear wall 71 ₃ of the rubbermember-accommodating portion 71 (see FIG. 9). Therefore, when a load ina longitudinal direction (exactly in the direction of the straight lineL₃ in FIG. 14) is applied to the upper mount 65, the entire projections75 and 77 are crushed and hence, the upper mount rubber member 74exhibits a relatively large rigidity. On the contrast, the convexportions 75 ₁, 75 ₁; 77 ₁, 77 ₁ (see FIG. 7 and 8) at the left and rightopposite ends of the upper two projections 75 and 77 are merely in pointcontact with the outer wall 71 ₄ and the inner wall 71 ₅ of the rubbermember-accommodating portion 71. When a load in a lateral direction(exactly in the direction of the arm L₃ in FIG. 14) is applied to theupper mount 65, the convex portions 75 ₁, 75 ₁; 77 ₁, 77 ₁ are easilycompressed, and hence, the upper mount rubber member 74 exhibits arelatively small rigidity. Namely, the rigidity of the upper mountrubber member 74 has an anisotropy and is higher in the direction of thestraight line L₂ and lower in the direction of the arc L₃ (in a tangentdirection about the phantom center point C).

A gap is provided between each of the lower two projections 76 and 78and the wall surface of the rubber member-accommodating portion 71, butwhen a large load in the lateral direction is applied to the upper mountrubber member 74 to largely deform it, the two projections 76 and 78 arebrought into contact with the wall surface of the rubbermember-accommodating portion 71 to exhibit a load-supporting function(see FIG. 8).

Next, the structure of the lower mount 66 will be described below withreference to FIGS. 11 to 13.

The mount block 64 is fitted over the lower end of the swivel shaft 62protruding downwards from the swivel case 60, and is fixed to the lowerend by two bolts 79, 79. Lower mount rubber members 80, 80 are mountedto cover outer periphery of the metal cores 64 ₁, 64 ₁ protrudinglaterally from the lower end of the mount block 64. A pair of left andright rubber member-accommodating portions 42 ₂, 42 ₂ are formed on arear surface of a lower end of the extension case 42, and a pair of leftand right cover members 81, 81 are fastened to the extension case 42 bybolts 82, 82 respectively in order to fix the lower mount rubber members80, 80 fitted into the rubber member-accommodating portions 42 ₂, 42 ₂from the rear.

The lower end of the extension case 42 is resiliently supported at thelower end of the swivel shaft 62 through the lower mount 66 providedwith the lower mount rubber members 80, 80.

Next, the operation of the present embodiment will be described belowmainly with reference to FIG. 14.

An inertia force a generated by the reciprocal movements of the pistons14, 14 in the direction of the straight line L₁ (in the longitudinaldirection) with the operation of the engine E is countervailed by aninertia force generated in the direction of the straight line L₁ by therotations of the counterweights 15 ₁ mounted on the crankshaft 15 withthe balance rate of 100%, and hence, the primary vibration in thedirection of the straight line L₁ is finally relatively small. However,lateral inertia forces c and d generated with the rotation of thecounterweights 15 ₁ of the crankshaft 15 vibrate the outboard enginesystem O in the direction of the arc L₃ (in the lateral direction) abouta phantom vibration center C, and such vibration is transmitted to thehull S through the mounting bracket 55.

The phantom vibration center C is a point on the engine E as a vibrationsource, which can be construed as being always not moved. The positionof the phantom vibration center C is moved depending on the operationalstate of the engine E, but a phantom vibration center C in a highrotational speed range (of 3,000 rpm or more) of the engine in which theanti-vibration performance of the engine E is particularly aconsideration, is contemplated in the present embodiment.

The above-described vibration of the engine E is transmitted from theupper mounts 65, 65 and the lower mount 66 through the mounting bracket55 to the hull S. During this time, the vibration is reduced by theupper mount rubber members 74, 74 of the upper mounts 65, 65 and thelower mount rubber members 80, 80 of the lower mount 66 and thus, thevibration transmitted to the hull S is weakened. Particularly, in thepresent embodiment, the lateral vibration is reduced effectively by theupper mounts 65, 65 closer to the engine E which is the vibrationsource.

More specifically, the vibration in the direction of the arc L₃ aboutthe phantom vibration center C is transmitted from the rubbermember-accommodating portions 71, 71 of the engine-supporting block 41supporting the engine E to the upper mount rubber members 74, 74 of theupper mounts 65, 65, but the upper mount rubber members 74, 74 areeasily deformed to effectively damp the vibration, thereby reducing thevibration transmitted to the mount arm 63, because the rigidity of theupper mount rubber members 74, 74 in the direction of the vibration (inthe direction of the arc L₃) are set at the lower value. Thus, it ispossible to reduce the vibration transmitted from the mount arm 63through the swivel shaft 62, the swivel case 60, the swinging arm 59 andthe mounting bracket 56 to the hull S to contribute to an enhancement inriding comfort.

The rigidity of the upper mount rubber members 74, 74 in the directionof the straight lines L₂, L₂ is set at the high value and for thisreason, the vibration in the longitudinal direction cannot be reducedeffectively. However, there is not a possibility that the vibration inthe longitudinal direction of the engine E may be transmitted throughthe upper mount rubber members 74, 74 to the hull S, because it issuppressed by the counterweights 15 ₁ of the crankshaft 15, as describedabove.

A portion of the lateral vibration not absorbed by the upper mountrubber members 74, 74 is transmitted from the metal cores 73, 73 to themount arm 63, but the swinging movement of the mount arm 63 due to thelateral vibration not absorbed by the upper mount rubber members 74, 74can be suppressed to the minimum, because the axis of the swivel shaft62 supporting the mount arm 63 for swinging movement is disposed on thearc L₃ extending the centers of the upper mount rubber members 74, 74.Thus, it is possible to suppress the transmission of the vibration tothe steering handlebar 67 coupled to the mount arm 63 to the minimum.

Meanwhile, to suppress the transmission of the vibration to the steeringhandlebar 67 to the minimum, it is desirable that the axis of the swivelshaft 62 supporting the mount arm 63 be disposed on the arc L₃ extendingthe centers of the upper mount rubber members 74, 74, as describedabove. However, to further alleviate the transmission of the vibrationto the hull S, it is preferable that the axis of the swivel shaft 62 bedisplaced longitudinally from the arc L₃. This is because if the axis ofthe swivel shaft 62 is displaced longitudinally from the arc L₃, themount arm 63 to which the lateral vibration not absorbed by the uppermount rubber members 74, 74 has been transmitted is swung about theswivel shaft 62 to function as an anti-vibration link in a sense,thereby alleviating the transmission of the vibration to the hull S.

Longitudinal thrusts e and f generated by the propeller 52 are alsotransmitted through the upper mount rubber members 74, 74 to the hull S.In this case, the longitudinal thrusts e and t can be transmittedeffectively to the hull S, because the rigidity of the upper mountrubber members 74, 74 in the directions of the straight lines L₂, L₂ isset at a high value. The directions of the straight lines L₂, L₂, inwhich the rigidity of the upper mount rubber members 74, 74 is largest,are offset from the directions of the thrusts e and t by the angles α,α, but the angles α, α do not exert a substantial influence, becausethey are relatively small. It is desirable from such meaning that theangles α, α be small and that the maximum values of the angles α, α besuppressed to a value equal to or smaller than 45°.

In the simple structure in which the rigidity of the upper mount rubbermembers 74, 74 of the upper mounts 65, 65 only has the anisotropy, asdescribed above, it is possible to ensure that the vibration of theengine E is hard to be transmitted to the hull S and the steeringhandlebar 67, while permitting the thrusts e and f generated by thepropeller 52 to be transmitted effectively to the hull S without theprovision of a special balancer device accompanied by the increase ofweight and cost.

Next, a second embodiment of the present invention will now be describedwith reference to FIGS. 15 and 16.

The second embodiment has a feature in the structure of a lower mount66. In the lower mount 66 in the first embodiment, the left and rightopposite ends of the mount block 64 have been retained by the pair ofcover members 81, 81, but in the second embodiment, a single covermember 81′ integrally formed is fastened to a rear surface of a lowerend of an extension case 42 by four bolts 82 to retain the mount block64. The cover member 81′ has no opening and covers the rear surface ofthe mount block 64 completely.

By fastening the single cover member 81′ to the rear surface of thelower end of the extension case 42 as described above, the extensioncase 4 and the cover member 81′ cooperate with each other to form abox-shaped structure with a horizontal section closed, leading to anenhanced rigidity. Thus, it is possible to firmly retain the mount block64 between the extension case 4 and the cover member 81′ to effectivelyprevent the generation of a resonance.

Although the embodiments of the present invention have been described indetail, it will be understood that various modifications in design maybe made without departing from the subject matter of the inventiondefined in claims.

For example, the 2-cylinder and 4-cycle engine has been illustrated inthe embodiments, but the present invention is also applicable to anothertype engine such as a single-cylinder and two-cycle engine.

INDUSTRIAL APPLICABILITY

As discussed above, the present invention is applicable to an outboardengine system including an engine having a crankshaft disposedvertically, and a cylinder axis disposed longitudinally.

What is claimed is:
 1. An outboard engine system comprising a systembody (41), an engine (E) mounted on said system body (41), a mountingmeans (55) which is detachably mounted to a hull (S), and a mount device(65) having a pair of left and right elastomeric members (74) forsupporting said system body (41) on said mounting means (55),characterized in that said engine (E) is disposed such that a crankshaft(15) is disposed vertically, and a cylinder head (12) is disposed toface rearwards with a cylinder axis disposed in a longitudinal directionparallel to a propeller shaft (53), and a rate of balance between thereciprocal inertia mass of a piston (14) and a rotational inertia massof the crankshaft (15) is set at approximately 100%; said elastomericmembers (74) are disposed on left and right opposite sides of the engine(E), and the rigidity of said mount device (65) is set so that therigidity in a tangent direction about a phantom center point (C) ofvibration in a high rotational speed range of the engine (E) is lowerthan the rigidity in a radial direction about the phantom center point(C) of vibration.
 2. An outboard engine system according to claim 1,wherein an angle (α) formed by a straight line (L₁) extending forwardsfrom said phantom center point (C) of vibration with a straight line(L₂) extending from said phantom center point (C) of vibration towardsaid elastomeric member (74) is smaller than 45°.
 3. An outboard enginesystem comprising a system body (41), an engine (E) mounted on saidsystem body (41), a swivel shaft (62) for pivotally supporting saidsystem body (41) on a hull (S), a mount arm (63) integral with saidswivel shaft (62), a mount device (65) having a pair of left and rightelastomeric members (74) for supporting said system body (41) on saidmount arm (63), and a steering handlebar (67) connected to said mountarm (63) to swing said system body (41) about said swivel shaft (62),characterized in that said engine (E) is disposed, so that a crankshaft(15) is disposed vertically, and a cylinder head (12) is disposed toface rearwards with a cylinder axis disposed in a longitudinal directionparallel to a propeller shaft (53), and so that a rate of balancebetween the reciprocal inertia mass of a piston (14) and a rotationalinertia mass of the crankshaft (15) is set at approximately 100%; saidelastomeric members (74) are disposed on left and right opposite sidesof the engine (E); the rigidity of said mount device (65) is set so thatthe rigidity in a tangent direction about a phantom center point (C) ofvibration in a high rotational speed range of the engine (E) is lowerthan the rigidity in a radial direction about said phantom center point(C) of vibration; and said swivel shaft (62) is disposed on an arc (L₃)of a circle extending through said elastomeric members (74) about saidphantom center point (C) of vibration.
 4. An outboard engine systemaccording to any of claims 1 to 3, further including a cover member(81′) fastened to a rear surface of a lower end of an extension case(42) connected to said system body (41) to define a space with ahorizontal section closed, and a mount block (64) which is mounted at alower end of said swivel shaft (62) and retained in said space.